Keyway strip for concrete pavement forms



United States Patent 3,166,815 KEYWAY STRIP FQR CONCRETE PAVEMENT FQRMS James A. Rappas, 202 Thornton Road, Rochester, N.Y. Filed Jan. 29, 1963, Ser. No. 254,724 5 Claims. (Cl. 25-418) This invention relates to the construction of pavements for concrete roads or streets, and more particularly to what may be called a keyway strip for attachment to the usual metallic forms which define an edge of the pavement strip being laid.

As well known, it is customary to lay a concrete pavement of two or more lanes, in a strip having a width of one lane (the lane having a width of about 8 feet to 12 feet, depending upon local preferences and practice) while using metallic forms at the edges of the first lane which is laid, and then lay a strip for the next succeeding lane, with the adjacent edge tight against the previously set concrete of the first lane, after the removal of the metallic form from the edge of the first lane. To minimize subsequent dilferences in elevation between the top surfaces of the adjacent lanes, due to frost heaves, softening of sub-grade, or other causes, it is customary not only to tie the adjacent strips to each other by bolts or tie-rods passing horizontally and laterally from one pavement strip into the next strip, but also to provide a small longitudinal keyway or channel formed in the vertical edge of the concrete strip which is laid first, so that When the second concrete strip is laid next to the first strip, a portion of the concrete of the second strip will flow into and fill the keyway or channel left in the first strip, somewhat like a tongue and groove joint used in wooden flooring and other kinds of lumber, so that the two concrete pavement strips are more firmly interlocked with each other and restrained against relative vertical movement.

It is to this phase or aspect of the laying of concrete pavement strips that the present invention relates. It has been proposed to make the metallic forms of the proper cross section to provide the keyway or channel in the edge of the concrete laid against such forms, but this is not satisfactory, especially for road building contractors who do an interstate business, because the specifications for the shape and size of the keyway do not always agree in different states, and forms which could be used in one state might not be suitable in another. Moreover, regardless of interstate activities of a particular contractor, there are certain situations where no keyway is wanted along the edge of a concrete strip to be laid, and for such situations the contractor would also have to provide plain forms without any built-in keyway configuration.

Therefore, it is most economical and has become customary to use plain forms for the edges of the concrete strip, and to apply separate keyway strips to the metal forms, which may be rolled metal, such as sheet metal of rather thick gauge rolled to bend them to the desired cross sectional shape. These keyway strips have been sometimes of wood, and sometimes of metal. When the concrete has set and the forms are to be removed from the edge of the set concrete, it is very difficult to remove the wooden or metallic keyway strips from the concrete without breaking the keyway strips or damaging See Another object is the provision of a tough, durable strip which is not likely to be damaged even if accidentally run over by a truck or other piece of moving equipment, and which can be used over and over again repeatedly.

Still another object is the provision of a keyway strip so designed and constructed that it can be easily and quickly applied to the usual metal form before the concrete is laid, and can be easily removed or stripped from the set concrete when the form is removed, without damage to the keyway strip or to the concrete.

A further object is the provision of a keyway strip so designed and constructed as to hug closely against the concrete form to which it is applied, to eliminate or minimize possible seepage of concrete between the keyway strip and the main portion of the form.

A still further object is the provision of a keyway strip so designed that when the form is removed from the set concrete, the ends of the keyway strip will tend to spring outwardly away from the form, to facilitate the easy stripping or removal of the keyway strip from the concrete.

Another object is the provision of a keyway strip so designed that successive lengths of such strip are held in accurate alinement with each other, and so that successive lengths are so connected with each other as to facilitate qiuck stripping from the set concrete.

These and other desirable objects may be attained in the manner disclosed as an illustrative embodiment of the invention in the following description and in the accompanying drawings forming a part hereof, in which:

FIG. 1 is a side elevation of an individual length of keyyay strip according to a preferred embodiment of the invention;

FIG. 2 is a side elevation, on a larger scale, of the adjacent portions of the ends of two keyway strips, showing details of the joint between them;

FIG. 3 is a transverse section taken approximately on the line 3-3 of FIG. 1, on a larger scale;

FIG. 4 is a similar transverse section taken approximately on the line 4-4 of FIG. 1; and

FIG. 5 is a fragmentary section through the edge portion of a newly laid concrete pavement, before the forms have been stripped therefrom, showing the conventional sheet metal form and the keyway strip of the present invention still in place against the concrete.

Referring first to FIG. 5, there is shown a portion of a conventional sheet metal form such as commonly used to define the edge of a concrete pavement which is to be laid. The sheet metal form comprises a horizontal bottom flange 11, a flat vertical flange 13, and a small horizontal top flange 15 which frequently forms a guideway or rail for supporting a concrete pavement laying machine as the laying machine travels slowly in a longitudinal direction along the forms at opposite edges of the roadway strip, in the familiar manner. However, the manner in which the concrete'is laid, whether by a machine travelling on the rail portion 15 or in any other manner, is immaterial so far as the present invention is concerned.

It is to the inner face ofthe vertical web 13 of the concrete form (that is, the face toward the right, viewed as in FIG. 5) that the keyway strip is to be applied, extending longitudinally along the form so that when the concrete is laid, the keyway strip will make a groove or channel extending longitudinally in the vertical edge of the newly laid concrete. In the past, the keyway strips have customarily been of wood or metal, and this has had the disadvantages already mentioned above.

According to the present invention, the keyway strip, indicated in general at 21, is of extruded plastic material having great strength. It is of generally trapezoidal shape,

having the specific dimensions required by the specifica tions applying to the job. The specific dimensions vary from locality to locality, but in general the base wall 23 of the trapezoid is about two and a half inches wide, the opposite face wall designated by the numeral 25 is about one and one half inches wide, and the thickness of the strip, between the outer faces of the two walls 23 and 25, is in the range of about five-eighths inch to one inch. The other edges of the trapezoid, designated by the numerals 27 and 29, are sloped at angles in the general range of about forty or fifty degrees.

The extruded plastic strip of the present invention is hollow in cross section, having the four external walls making up the outer shape of the trapezoid, plus preferably two strengthening Webs shown at 3i and 33, each of these webs 31 and 33 extending from what might be called the rear wall 23 to the front wall 25, and being set a little inwardly from the corners where the Wall 25 joins the sloping Walls 27 and 2%, respectively. This leaves, between the strengthening webs or flanges 31 and 33, a rectangular space which is open or unoccupied throughout most of the length of each keyway strip, but which is preferably occupied by a dowel member at the ends of the keyway strip, as further described below.

The conventional metallic forms 13, etc., are customarily provided in lengths of ten feet, each form strip having a plurality of holes spaced longitudinally along theform, for reception of bolts which initially hold the tie rods which serve to tie one concrete road strip to the next adjacent road strip for the next lane of traffic. In the most commonly used construction, there are three bolt holes in each ten foot length of metal form, the first bolt hole being substantially ten inches from one end of the form, the next hole being forty inches from the first one, the next holebe'ing another forty inches from the second one, this last hole being thirty inches from the opposite end of the form. Thus when the form strips are assembled end to end in the conventional manner, the bolt holes will be at uniform distances of forty inches from each other, but so far as any individual section of the form is concerned, the bolt holes closest to the respective ends of the section will be thirty inches from one end and ten inches from the other end. At these same distances which havebecome standard or conventional in the industry, the extruded plastic keyway strip of the present invention is provided with bolt holes, shown at 4 1 in FIGS. 1 and 4. Either before or after the metal form is set in the proper final location on the ground (but in any event before the concrete is poured, of course) the keyway strip 21 of the present invention is applied to the inner face of the vertical flange 13 of the form, and is held thereto by passing conventional bolts 43 through the above mentioned standard or conventional holes in the form flange 13 and on through the holes 41 in the key- Way strip, then screwing onto the inner ends of the bolts 43 the nuts 4-5, which are screwed home to such extent that they press firmly against the Wall 25 of the keyway strip and press the base of the key-way strip firmly and tightly against the face of the flange 13 of the form. The nuts 45 may be either separatefrom or formed integrally with the tie rod sections 4'7 which are provided, as usual, with angled ends 49. These tie rods 47, 49 are conventional in the industry, and are sometimes screwed into separate nuts 45 (which nuts thus receive the bolts 43 at one end, and the tie rods 47 at the other end) and sometimes are formed with the nut portions 45 integrally attached. Whichever form of tie rod is used, is immaterial for purposes of the present invention, as in either event the nut portion 45 serves initially to hold the keyway strip 21 tight against the face 13 of the form, and later the nut 45 and tie rod 47 remain permanently embedded in the concrete. I

It has been mentioned above that the keyw ay strip of the present invention is preferably formed of extruded plastic material. It is preferred to make it of-polyvinyl plastic rather than polyethylene plastic. The polyethylene plastic would be excellent from the standpoint of pulling away readily from the set concrete when the forms are stripped, but polyvinyl chloride is easier to extrude in the desired shape, and so it is preferred to use this material. A specific polyvinyl chloride which has been found excellent for making the extruded strip is the material available commercially on the market fro-m B. P. Goodrich Chemical Company, of Cleveland, Ohio, and identified as B. E. Goodrich No. 8714 Goon virgin rigid vinyl, or identified as Crane plastics code No. (3-1400. Extruded strips of this material, having the form and dimensions as herein disclosed, are extremely tough, and it is found in practice that if a strip of this kind accidentally lies on the ground and is run over by a heavy truck, it is not damaged and can still be used again. Moreover, trips of this kind will withstand repeated handling and repeated stripping from the concrete, and can be used over and over again many times, thus being very economical in use.

Another preferred feature of the present invention is that the outside face of the rear wall 23 of the strip is preferably not entirely flat or plane, but is slightly concave or bowed as shown in N65. 3 and 4. Thus when assembling the concrete forms, the tightening of the nuts 45 on the bolts 43 will draw the top and bottom edges of the keyway strip tight against the face of the portion 13 of the metal form, leaving no gap into which any of the fresh concrete can seep. Seepage of concrete into small spaces between the lteyway strip and the metal form has been a frequent occurrence and a common cause of complaint when using the conventional wooden keyway strips, and apparently no satisfactory way to prevent occasional gaps between the wooden strip and the metal form has been devised. Testing of the extruded plastic strip of the present invention, made with the slightly bowed rear wall as above described, has proven that normally there is no seepage of concrete behind the keyway strip, and therefore no concrete has to be chipped away laboriously when the poured concrete has set and the forms are to be removed.

Another preferred feature of the present invention is that there is not only the above described transverse or lateral bow or slight concavity in the strip, but also the strip is slightly bowed in a lengthwise or longitudinal direction, to the extent of bowing a distance of about eight inches in the strip length of ten feet. The bow is in such direction that if the base wall 23 of the strip is laid on a level floor, with the wall 25 uppermost, the ends of the strip (in :the conventional ten foot length) will rest on the level floor and the mid-point of the strip will be elevated about eight inches from the floor. This bowing of the strip in the longitudinal direction is accomplished by proper design of the extruding die in a manner well understood in the art of plastics extrusion.

This longitudinal bowing of the keyway strip serves two purposes. First, it will be remembered that at one end of the strip the closest bolt hole is thirty inches from the end. With the above described slightly bowed shape of the strip, the tightening of the bolt thirty inches from the end of the strip serves to press the free or unsupported portion of the strip, beyond the final bolt, firmly against the metal form, so as to eliminate or minimize the seepage of concrete between the keyway strip and the form. Second, the bowing of the strip in a longitudinal direction serves the further purpose that when the bolts 43 are loosened and the metal forms are removed from the edge of'the set concrete, the ends of each keyway strip wil tend to spring horizontally outwardly away from the concrete, to resume the set or bowed shape of the keyway strip. This enables the ends of the keyway strip to be readily grasped for the purpose of pulling the strip laterally away from the set concrete.

Another preferred feature of the present construction is the provision of dowel members, as already previously mentioned above, which serve to hold adjacent ends of different strips in accurate alinement with each other. As shown in FIGS. 1, 2, and 3, each dowel member 51 is in the form of a bar of preferably rectangular crosssection, of proper dimensions to fit rather snugly in the rectangular space between the webs 31 and 32 and the walls 23 and 25. Conveniently, each dowel member is about five inches long, having about three inches extending into an end of one keyway strip and permanently anchored therein as by means of staples 53 (FIG. 2) driven through the wall 23 or the wall 25 or both and extending into the material of the dowel member 51. The remaining two inches of the length of the dowel member projects beyond the end of the keyway strip in which it is anchored, and is thrust longitudinally into the corresponding rectangular space of the next adjacent keyway strip when the keyway strips are assembled in end to end relation to each other. It does not matter in which end of the keyway strip the dowel 51 is anchored, but it should be the same end with respect to all of the keyway strips, so that successive strips can be properly assembled, bearing in mind that the bolt holes 41 are not symmetrical with respect to the ends of the strip.

The dowel, like the strip itself, is preferably made of plastic material, but need not be of the same material from which the keyway strip is made. It may be, for example, either of the same polyvinyl chloride material above mentioned with respect to the keyway strip, or of any other polyvinyl chloride composition, or of any suitable polyethylene composition. The projecting end of the dowel member preferably has its corners chamfered as shown at 55 in FIG. 2, for easier insertion into the end of the next adjacent keyway strip. A dowel member for a typical size and shape of keyway strip might have cross-sectional dimensions, for example, of three-eighths inch by seven-eighths inch. The use of these dowels helps to hold adjacent strips in proper position, and especially to hold the thirty inch length of strip (beyond the last bolt) in proper position, because the end of the next adjacent strip is only ten inches from its next bolt hole, and therefore is held more rigidly than an end which is thirty inches from its next bolt hole. The use of dowel connecting what might be called the ten inch end of one strip to what might be called the thirty inch end of the next adjacent strip, serves to impart some of the rigidity of the ten inch end to the thirty inch end of the next strip, assuring proper holding of the parts.

The details of use of keyway strips of this kind will be readily apparent to those skilled in this type of concrete construction. For the benefit of others it may be said, however, that after assembling the metal forms which are to define the edge of the concrete pavement, and the keyway strips, in the manner already mentioned above, the concrete is poured or placed as indicated schematically at 61 in FIG. 5. After sufiicient time has elapsed for the concrete to set or harden, the bolts 43 are removed, and any stakes or other fastenings holding the forms immovably to the ground are also removed, and then the forms 11, 13, 15 can be stripped from the hardened concrete, either by pulling them laterally away, or by lifting them vertically upwardly, or by a combination of both motions. The nuts 45 and the tie rods 47 remain permanently in the hardened concrete.

When the metal forms 13, etc., are removed from the edge of the set concrete, the plastic keyway strips will tend to spring outwardly away from the edge of the con crete, at their ends, on account of the above mentioned longitudinal bow or set which has been built into the keyway strips. The ends are then grasped, and the key way strip is pulled laterally away from the set concrete and is then ready to be used again wherever required during the further progress of the pavement laying operation. If the keyway strip remains stuck in the hardened concrete and its ends do not spring out by themselves, one end of the strip can easily be pried out of its groove in the concrete, by inserting a small bar or prying tool into one of the openings at the exposed end of the strip. When dowels 51 are used, as in the preferred construction, then it is very easy to remove the keyway strips even if they do not start to spring out from the concrete groove by themselves, because when one strip is pulled laterally away, the dowel member will cause the next adjacent strip to start to pull out, and so on, the action proceeding continuously from strip to strip until the entire required length of keyway stripping is removed.

Then the next adjacent portion of the roadway is laid, putting up any desired form to define the far edge of the new pavement, but no form being used at the near edge adjacent to the concrete 61 already laid and hardened. Before the next width of concrete is laid, tie rods are screwed into the nuts 45 which are already embedded in the concrete, these nuts being accessible, of course, now that the bolts 43 and keyway strips 21 have been removed. Then the new concrete is poured or otherwise placed, encompassing or enveloping the new tie rods which have been screwed into the nuts 45, and also projecting into and filling the longitudinal groove which has been left in the original concrete where the keyway strip 21 has been removed. Thus the next width or lane of concrete is laterally tied to the previously laid lane by the tie rods, and is keyed or anchored to the previously laid lane against vertical movement relative thereto, by means of the projection on the second lane extending into the longitudinal keyway or groove in the first lane.

Another advantage of the present construction is that it can be readily sawed by a conventional carpenters hand saw. If a portion of the length of one strip is damaged, the damaged part can be sawed off, and the undamaged part can be spliced to another length of keyway strip by using a dowel of any desired length. Also the bolt holes 41 may be readily drilled at any required locations by a conventional hand augur. A conventional wooden keyway strip may also be sawed and drilled, but as a practical matter it can not be spliced with a dowel. A metallic keyway strip can not be cut to separate a damaged portion from an undamaged portion, nor be drilled for bolt holes, without using special equipment, nor can it be spliced readily.

It is seen from the foregoing disclosure that the objects and purposes of the invention are well fulfilled. It is to be understood that the foregoing disclosure is given by way of illustrative example only, rather than by way of limitation, and that without departing from the invention, the details may be varied within the scope of the appended claims.

What is claimed is:

1. The combination with an upright form for defining the lateral edge of a concrete pavement to be laid, of a keyway strip attached to a face of said form and extending longitudinally along the form in position to cause a keyway groove in the edge of such concrete pavement, said keyway strip being characterized by the fact that it is formed of plastic material of generally trapezoidal external cross section, and that it is hollow, having a plurality of longitudinally extending cavities separated from each other by a strengthening web, said keyway strip being further characterized by the fact that the external face thereof which is engaged with said upright form is slightly concave in cross section, so that the upper and lower edges thereof will tightly engage said upright form to prevent freshly poured concrete from seeping between the keyway strip and the upright form.

2. The combination with an upright form for defining the lateral edge of a concrete pavement to be laid, of a -keyway strip attached to a face of said form and extending longitudinally along the form in position to cause a keyway groove in the edge of such concrete pavement, said keyway strip being characterized by the fact that it is formed of plastic material of generally trapezoidal external cross section, and that it is hollow, having a plurality of longitudinally extending cavities separated from each other by a' strengthening web, said keyway strip being further characterized by the fact that it is slightly resilient and, initially bowed in a longitudinal direction to such extent that when the upright form is stripped from solidified concrete poured against it, the ends of the keyway strip will tend to spring laterally outwardly away from the solidified concrete.

3. As a new article of manufacture, a keyway strip adapted for attachment to a flat face of an upright form to be used for defining an edge of a concrete pavement -to be laid, said keyway strip being formed of plastic material and having a generally trapezoidal hollow shape in cross section with a rear wall, a front wall approximately parallel'to the rear, wall, sloping end walls connecting the rear wall to the front wall and converging toward'each other in a direction from the rear wall toward the front wall, two strengthening webs extending between the rear wall and the front wall in locations spaced laterally from eachother, and a plurality of bolt holes extending transversely through said front and rear walls at predetermined intervals spaced longitudinally along said keyway strip, said bolt holes having diameters no greater than the lateral separation between said strengthening webs and being so placed as to be out of alinement with said strengthening webs, further including a dowel memher having one end portion extending into and permanently anchored in the space between said two strengthening Webs at one end of the keyway strip, said dowel member having an opposite end portion projecting beyond the end of the keyway strip and adapted to enter the corresponding space at one end of another keyway strip which is to be longitudinally alined with the lteyway strip in which the dowel member is anchored.

4. A construction as defined in claim 3, in which the external face of said rear wall is slightly concave in a transverse direction and also is slightly bowed concavely in a longitudinal direction.

5. A construction as defined in claim 4, in which said keyway strip is formed mainly of polyvinyl chloride plastic material.

References Cited by the Examiner UNITED STATES PATENTS 1,629,750 5/27 Weller 25-118 2,453,223 11/48 Henderson. 2,611,169 9/52 Torrelli 25-118 2,745,165 5/56 Lewis 25-118 2,772,468 12/56 Heltzel 25118 2,953,835 9/60 Armstrong et al. 2,985,938 5/61 Rappas.

MICHAEL V. BRINDISI, Primary Examiner. 

1. THE COMBINATION WITH AN UPRIGHT FROM FOR DEFINING THE LATERAL EDGE OF A CONCRETE PAVEMENT TO BE LAID, OF A KEYWAY STRIP ATTACHED TO A FACE OF SAID FORM AND EXTENDING LONGITUDINALLY ALONG THE FORM IN POSITION TO CAUSE A KEYWAY GROOVE IN THE EDGE OF SUCH CONCRETE PAVEMENT, SAID KEYWAY STRIP BEING CHARACTERIZED BY THE FACT THAT IT IS FORMED OF PLASTIC MATERIAL OF GENERALLY TRAPEZOIDAL EXTERNAL CROSS SECTION, AND THAT IT IS HOLLOW, HAVING A PLURALITY OF LONGITUDINALLY EXTENDING CAVITIES SEPARATED FROM EACH OTHER BY A STRENGTHENING WEB, SAID KEYWAY STRIP BEING FURTHER CHARACTERIZED BY THE FACT THAT THE EXTERNAL FACE THEREOF WHICH IS ENGAGED WITH SAID UPRIGHT FROM IS SLIGHTLY CONCAVE IN CROSS SECTION, SO THAT THE UPPER AND LOWER EDGES THEREOF WILL TIGHTLY ENGAGE SAID UPRIGHT FORM TO PREVENT FRESHLY POURED CONCRETE FROM SEEPING BETWEEN THE KEYWAY STRIP AND THE UPRIGHT FORM. 